Slots are arranged in an outer circumferential side of a rotor core of a squirrel-cage induction motor, and a rod-shaped rotor conductor is inserted in each of the slots. Ring-like conductors termed “short-circuiting rings” are connected to both ends of the rotary conductors inserted into each of the slots to form a squirrel-cage-shaped rotor conductor (squirrel-cage rotor). An induced voltage is generated in the rotor conductor due to intersection between the rotary magnetic field generated by stator coils and the rotor conductors within the rotor core slots. Due to the generated induced voltage, induced current flows in the rotor conductors forming a closed circuit, and magnetic poles are generated in the rotor core. A circumferential force is generated in the rotor due to the interaction between the magnetic poles of the rotor core and the magnetic poles of the rotary magnetic field. This force results in output torque of the rotor shaft of the induction motor.
The rotor conductor deforms due to rapid changes in the current induced by the rotary magnetic field, and the rotor conductor expands and contracts due to temperature changes due to the induced current. Further, the rotor conductor is affected by centrifugal force due to rotation and by external vibrations. Such deformation, expansion-contraction, centrifugal force, vibration, and the like of the rotor conductor generate movement of the rotor conductor relative to the rotor core.
To prevent relative movement between the rotor conductor and the rotor core, a shimming operation termed “swaging” is performed for fixing the rotor conductors relative to the slots of the rotor core. In this operation, a driving-in slot to be driving into by a chisel is provided in a transverse direction-central portion of the outer circumferential surface of the rotor conductor inserted in the rotor core slot. Due to this operation, the outer circumferential side of the rotor conductor expands in the slot transverse direction to form a flared portion. The expanded flared portion is in a state in which the expanded flared portion performs propping between the internal wall surfaces of either side of the rotor core slot, and due to the force of propping between the rotor conductor and the inner wall surfaces of the rotor core slot, the rotor conductor is fixed to the rotor core slot.
For example, Patent Literature 1 discloses a squirrel-cage induction motor in which a rotor conductor inserted in the rotor core slot is fixed by forming a driving-in slot in the rotor conductor (in particular, see FIG. 1 and FIG. 2). In this squirrel-cage induction motor, a first driving-in slot, which is a deep slot having a certain length, is arranged near the axial-direction central portion of the outer circumferential surface of the rotor conductor as a driving-in slot for securely fixing the rotor conductor to the rotor core slot. Further, a second driving-in slot, which is shallower than the first driving-in slot, is arranged at a position other than the vicinity of the axial-direction central portion of the outer circumferential surface of the rotor conductor. The rotor conductor expanded in the transverse direction during the forming of the first and second driving-in slots is fixed in a state in which the rotor conductor performs propping between both side wall surfaces of the rotor core slot. This portion fixing the rotor conductor is termed the “fixing portion”.